This invention concerns a self-baking electrode, or Sxc3x6derberg electrode, intended for an electric arc furnace, in particular a furnace for producing metallurgical silicon, comprising a central column made up of a succession of pre-baked electrodes in carbon or graphite, an outer metal ferrule and carbon paste undergoing baking between the central column and the ferrule.
The principle of the self-baking electrode has been known since 1917 under a patent filed by Det Norske Aktieleskap for Elektrokemisk Industri (FR 488778) and its inventor C. W. Sxc3x6derberg gave it his name. The electrode is baked in the electric furnace itself using a carbon paste that is continually supplied inside a ferrule in steel comprising fins to support the electrode. With this technique, the lower part of the ferrule dissolves in the bath of molten metal imparting iron to the bath, which may be a hindrance in particular in the case of silicon.
To avoid contamination by iron, several solutions have been put forward which all consist of mechanically detaching the electrode and the ferrule so that the electrode can be caused to slide without the ferrule. It suffices to use a smooth ferrule without fins, but in this case a mechanical assembly must be provided so that the weight of the electrode can be given other support. This assembly is generally a piece inserted in the paste during baking, which consumes itself at the same time as the electrode, for example a strip of perforated steel as in patent IT 606568 filed in 1959 by the Edison company, or a column which forms a prebaked electrode in carbon or graphite, made up of elements assembled together by means of nipples as in patent U.S. Pat. No. 457,856 by J. A. Persson filed in 1984. Patent FR 2683421, filed by the Carburos Metallicos company describes various adaptations of this technique. Patent FR 2724219 by Pechiney Electrometallurgie proposes the suspension of the central column from a support that is vertically mobile over a distance that is greater than the length of each of the unit elements forming the central column.
The purpose of the invention is the improve this latter system such as to provide greater safety and increased reliability in the functioning of the electrode, by improving the assembly of elements forming the central column.
The subject of the invention is a system for the assembly of a self-baking composite electrode for electric arc furnaces, this electrode comprising an outer metal ferrule, a central column in pre-baked carbon or graphite formed of a plurality of elements assembled by nipples, and carbon paste placed between the ferrule and the central column, this system comprising a support that is vertically mobile over a distance that is greater than the length of each of the elements and is used to suspend the central column, and a temporary blocking device for the column, characterised in that it is equipped with a mechanism which, in co-operation with the temporary blocking device for the column, permits the application of a clamping torque of pre-set value between a new element and the central column to which this new element is to be screwed.